The invention relates to methods and arrangements for cleaning filters and more specifically to those methods and arrangements that include a pump for pumping a liquid through a filter medium located within a sealed container, and in which the pump can be reversed when a predetermined condition is fulfilled so that pollutants from the filter are transported to a collection unit.
In many technical fields there exists a strong wish to reduce emissions and leakage of environmentally harmful vapors and liquids. Today a number of different pumps, filters and valves, placed outside a container or tank, are used when pumping a liquid from the container or tank. Traditionally this has been done to make the equipment easily accessible for service and replacement of components. A problem with this arrangement is that there are a multitude of joints and connections between the various components where emissions may escape.
An area of particular interest is vehicles, which are provided with a number of containers and tanks containing substances that are more or less harmful to the environment. One example is fuel tanks, where fuel is pumped from a tank to the engine via one or more valves and at least one fuel filter. A fuel filter may be a source of problems and requires regular changing or cleaning, if pollutants such as particles have been introduced into the tank.
Replacing such a filter often entails a leakage of fuel to the surroundings if the fuel line is not emptied of fuel prior to changing the filter, or if the change is not properly performed and results in leaking connections.
According to an alternative solution the filter can be cleaned without being removed. An example of how a filter may be cleaned in this way is disclosed in SU-A-1 176 922, which shows a separate pump that reverses the flow in the filter. Any pollutants are flushed into a collecting tank in which the polluted fuel may be taken care of. A drawback with this system is that a number of additional components, with corresponding connections, are required, all of which constitute a potential sources of leakage.
The problem is solved by using an arrangement for cleaning filters according to the attached claims. The arrangement includes a pump for pumping a liquid through a first filter and is placed within a sealed container whereby the pump can be reversed when a predetermined condition is fulfilled so that pollutants from the first filter are transported to a collection unit.
For certain operating conditions, the arrangement may also be provided with a pressure regulating valve arranged to limit the pressure of the delivered liquid.
By placing as many components as possible within the container, the problem of leakage to the surroundings can be minimized significantly, as the number of connections to the outside of the container is reduced to a minimum; for example, a filler pipe and an outlet conduit.
The pump has a first suction conduit for normal operation that is provided with a non-return valve preventing flow back into the container when the pump is reversed. When the filter is to be cleaned, a second suction conduit, connected between the pressure regulating valve and the first filter, is used, which conduit is provided with a second filter and a non-return valve preventing flow back into the container. In this embodiment, the liquid in the container itself is used for cleaning the filter. In order to prevent pollutants and particles from being sucked into the wrong side of the first filter, the second filter should be as fine as, or finer than the first filter.
According to an alternative embodiment, the second suction conduit may be connected from the outer wall of the container to a position between the pressure regulating valve and the first filter. In this way a pre-filtered fluid or a fluid having particular cleansing or pollutant dissolving properties can be flushed through the first filter, thus eliminating the need for a second filter.
It may not be suitable to flush pollutants and particles removed from the first filter directly back into the container. According to a further embodiment, the arrangement may be provided with a collection unit in the form of a third filter placed in the container. This filter is connected to the first suction conduit of the pump via a non-return valve preventing flow towards the pump. In order to collect as many pollutants and particles as possible from the first filter, the third filter should be as fine as, or finer than the first filter.
According to an alternative embodiment, the collection unit may be placed outside the container, whereby polluted liquid is pumped to the unit via a conduit connecting the suction conduit of the pump and the outer wall of the container. In this way pollutants may be removed from the container altogether and the third filer can be eliminated. In the case of the above-mentioned embodiment where the suction conduit is connected to the outer wall, alternative cleansing and dissolving fluids, which normally cannot be mixed with the liquid in the container in greater quantities, may be used. Both pollutants and solvents can then be pumped out of the container and be disposed of safely.
The timing for cleaning the filter may be chosen in several ways. According to one embodiment, pressure sensors are used to measure the pressure drop across the filter, whereby a control unit starts the cleaning procedure when the pressure drop exceeds a certain level. It is also possible to measure this power consumption required for maintaining a certain delivery pressure, whereby cleaning starts when the required power exceeds a set limit. If the container is a fuel tank for a vehicle, a further condition to be fulfilled is that the engine of the vehicle must be switched off.
An alternative embodiment is that the condition for cleaning is fulfilled when a predetermined amount of liquid has passed through the filter, which can be measured by means of a flow meter. If the container is a fuel tank for a vehicle, a further embodiment is that the condition is fulfilled when the vehicle has traveled a certain distance.
The invention also relates to a method for cleaning filters in a sealed container for liquids, by means of the above described embodiments.